A conventional process for producing ceramic multilayer substrates is described, for example, in German Patent No. 43 09 005. In this conventional process, green ceramic foils (i.e., flexible, unfired ceramic foils in its raw state) are provided with printed circuit traces and plated contactings, also referred to as vias. In the first step of the conventional process, holes for the plated contactings are punched into the green ceramic foils. Printed circuit traces are then printed with a conductive paste on the ceramic foils using commonly known screen-printing technique. The punched holes for the vias are either filled with conductive paste during the printing of the printed circuit traces or in a printing operation carried out separately before the printing of the printed circuit traces. This method is also used for producing LTCC substrates (low temperature co-fired ceramics) which differ from other ceramic multilayer substrates in that ceramic foils are used which can already be fired at temperatures below 900.degree. C. Given these low sintering temperatures, very inexpensive conductive pastes can be used to produce the printed circuit traces. After imprinting the ceramic foils, they are dried and arranged one upon the other in a stack. The stack thus formed is subsequently laminated and finally fired.
The conductive pastes used in the present related art for producing ceramic multilayer substrates contain organic, highly volatile solvents which partially diffuse into the green ceramic foils. Such solvents are alcohols or terpineols, for example. After the printing of the printed circuit traces or the plated contactings but before the stacking and firing of the green ceramic foils, the ceramic foils must in conventional processes be dried in a drier since the conductive paste applied on the ceramic foils cannot be baked undried into the foils, otherwise a spontaneous vaporization of the solvent, contained in the conductive paste, at the high firing temperatures of the ceramic foils would lead to the formation of cracks and bubbles in the ceramic multilayer substrates. In this context, it must be regarded as extremely disadvantageous that the drying process of the green ceramic foils represents an exceedingly costly interruption of the manufacturing process. The individual ceramic foils are dried at slightly elevated temperatures until the predominant portion of the solvent has vaporized. Furthermore, with the evaporation of the solvent from the conductive paste and the evaporation of the solvent diffused into the ceramic foils comes a disadvantageous shrinkage of the printed circuit traces and ceramic foils. Since the ceramic foils do not all shrink uniformly, distortions can occur in the pattern of the printed circuit traces on the green ceramic foils. During the stacking of the ceramic foils subsequently carried out after the drying process, misalignments and displacements between the printed circuit traces and plated contactings of two ceramic foils located one upon the other can partially or totally prevent the occurrence of an electrical contact at the desired positions. Because of this, the multilayer substrate formed after the firing becomes unusable.